In recent years, an active matrix liquid crystal display device, for example, is used for various purposes for its beneficial features of compact, light-weight, low power consumption, etc. In such a display device, a display image can be rotated on a display screen in order to respond to a demand for the larger number of display functions.
Japanese Unexamined Patent Publication No. 7-175444/1995 (Tokukaihei 7-175444, published on Jul. 14, 1995) discloses a conventional arrangement for rotating the display image (a first conventional technique). With the first conventional technique, a frame memory once records each of horizontal and vertical data corresponding to image information of a video signal, and then converts the recorded horizontal and vertical data so as to be shifted in horizontal and vertical directions, thereby rotating the image information to be supplied to the display device.
Another conventional arrangement is a liquid crystal display device using a rotation controller 101, as shown in FIG. 7. As shown in FIG. 7, in the liquid crystal display device, liquid crystal drive circuits 103 and 104 are respectively provided along adjacent sides of a liquid crystal display panel 102, and the liquid crystal drive circuits 103 and 104 are respectively connected to the rotation controller 101. Each of the liquid crystal drive circuits 103 and 104 can operate both as a source drive circuit and a gate drive circuit. The rotation controller 101 supplies to the liquid crystal drive circuits 103 and 104 (a) an enable signal via control signal lines 105 and 106, respectively, and (b) an address control signal or a data signal via address and data signal lines 107 and 108, respectively. Further, operations of the rotation controller 101 are controlled by a liquid crystal controller 109.
As shown in FIG. 8, the active matrix liquid crystal display panel 102 includes (a) a plurality of a pair of a row gate bus line 111 and a row source bus line 112 which are connected to the liquid crystal drive circuit 104, and (b) a plurality of a pair of a column source bus line 121 and a column gate bus line 122 which are connected to the liquid crystal drive circuit 103. Further, (a) the row gate and source bus lines 111 and 112 and (b) the column source and gate bus lines 121 and 122 are arranged in a matrix, and a pixel is formed in a vicinity of an intersection of (a) the row gate and source bus lines 111 and 112 and (b) the column source and gate bus lines 121 and 122.
Each of the pixels has an identical arrangement. Each of the pixels is provided with a first MOS transistor 131 for displaying an original erect image, a second MOS transistor 132 for displaying a rotated image, a liquid crystal 133, and an auxiliary capacitor 134, as shown in the circuit diagram. A gate terminal of the first MOS transistor 131 is connected to the row gate bus line 111, whereas a gate terminal of the second MOS transistor 132 is connected to the column gate bus line 122. At the first MOS transistor 131, one of a source terminal and a drain terminal is connected to the column source bus line 121, and the other of the source terminal and the drain terminal is connected to one terminal of the liquid crystal 133 and to one terminal of the auxiliary capacitor 134. At the second MOS transistor 132, one of a source terminal and a drain terminal is connected to the one terminal of the liquid crystal 133 and to the one terminal of the auxiliary capacitor 134, and the other of the source terminal and the drain terminal is connected to the column source bus line 112. Other terminals of the liquid crystal 133 and of the auxiliary capacitor 134 are connected to a common electrode.
In the arrangement, when an image shown in FIG. 5(a) is displayed on the liquid crystal display panel 102, for example, the liquid crystal drive circuit 103 operates as the source drive circuit and the liquid crystal drive circuit 104 operates as the gate drive circuit in response to the control signal supplied from the rotation controller 101 via the control signal lines 105 and 106. Accordingly, the rotation controller 101 supplies the data signal to the liquid crystal control circuit 103, and then the liquid crystal control circuit 103 outputs the data signal to each of the column source bus lines 121. Further, the rotation controller 101 supplies the address control signal to the liquid crystal drive circuit 104, and accordingly the liquid crystal drive circuit 104 sequentially outputs an address signal to each of the row gate bus lines 111. As a result, the image shown in FIG. 5(a) is displayed on the liquid crystal display panel 102.
On the other hand, as shown in FIG. 5(b), when the image shown in FIG. 5(a) is rotated 90 degrees, the liquid crystal drive circuit 103 operates as the gate drive circuit and the liquid crystal drive circuit 104 operates as the source drive circuit in response to the control signal supplied from the rotation controller 101 via the control signal lines 105 and 106. Accordingly, the rotation controller 101 supplies the data signal to the liquid crystal control circuit 104, and then the liquid crystal control circuit 104 outputs the data signal to each of the row source bus lines 112. Further, the rotation controller 101 supplies the address control signal to the liquid crystal drive circuit 103, and accordingly the liquid crystal drive circuit 103 sequentially outputs the address signal to each of the column gate bus lines 122. As a result, an image shown in FIG. 5(b) is displayed on the liquid crystal display panel 102.
As described above, in the arrangement of the second conventional technique, the liquid crystal display panel 102 displays the image and rotates the display image in such a manner that the rotation controller 2 outputs the data signal, the address control signal and the control signal to the liquid crystal drive circuits 103 and 104.
Japanese Unexamined Patent Publication No. 10-319915/1998 (Tokukaihei 10-319915, published on Dec. 4, 1998) discloses a further conventional arrangement (a third conventional technique). In the arrangement of the third conventional technique, a plurality of row bus lines 131 and a plurality of column bus lines 132 are arranged in a matrix, and a pixel is provided in a vicinity of each intersection of the row bus lines 131 and the column bus lines 132, as shown in FIG. 9.
In each pixel, at a first MOS transistor 133 for displaying the erect image, a gate terminal is connected to the row bus line 131, one of a source terminal and a drain terminal is connected to the column bus line 132, and the other of the source terminal and the drain terminal is connected to one terminal of a liquid crystal 135 and to one terminal of an auxiliary capacitor 136 via a second MOS transistor 134. Further, at a third MOS transistor 137 for displaying the rotated image, a gate terminal is connected to the column bus line 132, one of a source terminal and a drain terminal is connected to the row bus line 131, and the other of the source terminal and the drain terminal is connected to the one terminal of the liquid crystal 135 and to the one terminal of the auxiliary capacitor 136 via a fourth MOS transistor 138.
The second MOS transistor 134 connected in series with the first MOS transistor 133 is provided so as to prevent electric charges (data), which are charged to the liquid crystal 135 via the third and fourth MOS transistors 137 and 138, from being discharged when the first MOS transistor 133 is switched ON. Likewise, the fourth MOS transistor 138 connected in series with the third MOS transistor 137 is provided so as to prevent electric charges (data), which are charged to the liquid crystal 135 via the first and second MOS transistors 133 and 134, from being discharged when the third MOS transistor 137 is switched ON.
However, in the arrangement of the first conventional technique using the frame memory, a high-speed memory having a large capacitance is required as the frame memory, thereby increasing a cost and a size of the display device.
Further, in the method of the second conventional technique using the rotation controller 101, the liquid crystal display panel 102 needs to be provided with the row source bus line 112 and the column gate bus line 122 in addition to the row gate bus line 111 and the column source bus line 121. This lowers an open area ratio of the pixel, thus degrading the display quality.
Further, in the arrangement of the third conventional technique, the pixel of the liquid crystal display panel requires the second and fourth MOS transistors 134 and 138 in addition to the first and third MOS transistors 133 and 137, and further requires control lines for ON/OFF control of the second and fourth MOS transistors 134 and 138. Thus, as in the second conventional technique, the second and fourth MOS transistors 134 and 138 as well as the control lines lower the open area ratio of the pixel. Further, many MOS transistors, etc. formed at each pixel cause problems such as lowering of yield in a manufacturing process.